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Date: Fri, 1 Jul 2011 18:30:03 +0100
From: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
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Subject: Re: [Qemu-devel] [PATCH v3] xen: implement unplug protocol in
 xen_platform
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To: Kevin Wolf <kwolf@redhat.com>
Cc: "xen-devel@lists.xensource.com" <xen-devel@lists.xensource.com>, "mst@redhat.com" <mst@redhat.com>, "armbru@redhat.com" <armbru@redhat.com>, Stefano Stabellini <Stefano.Stabellini@eu.citrix.com>, "qemu-devel@nongnu.org" <qemu-devel@nongnu.org>, "agraf@suse.de" <agraf@suse.de>, Anthony Perard <anthony.perard@citrix.com>

On Fri, 1 Jul 2011, Kevin Wolf wrote:
> Am 30.06.2011 16:16, schrieb Stefano Stabellini:
> > On Thu, 30 Jun 2011, Kevin Wolf wrote:
> >>> +static int pci_piix3_xen_ide_unplug(DeviceState *dev)
> >>> +{
> >>> +    PCIDevice *pci_dev;
> >>> +    PCIIDEState *pci_ide;
> >>> +    DriveInfo *di;
> >>> +    int i = 0;
> >>> +
> >>> +    pci_dev = DO_UPCAST(PCIDevice, qdev, dev);
> >>> +    pci_ide = DO_UPCAST(PCIIDEState, dev, pci_dev);
> >>> +
> >>> +    for (; i < 3; i++) {
> >>> +        di = drive_get_by_index(IF_IDE, i);
> >>> +        if (di != NULL && di->bdrv != NULL && !di->bdrv->removable) {
> >>> +            DeviceState *ds = bdrv_get_attached(di->bdrv);
> >>> +            if (ds) {
> >>> +                bdrv_detach(di->bdrv, ds);
> >>> +            }
> >>> +            bdrv_close(di->bdrv);
> >>> +            pci_ide->bus[di->bus].ifs[di->unit].bs = NULL;
> >>
> >> Have you tested if this is enough if the guest tries to continue using
> >> the device? I don't know of any case where it's not sufficient, just
> >> trying to make sure that it's really true in practice.
> > 
> > The purpose of this is to "hide" the disk from the guest. The unplug is
> > supposed to happen *before* the guest enumerates the IDE disks; it is
> > responsibility of the guest to make sure of it.
> > I tested it with Linux PV on HVM drivers, and Linux doesn't see the
> > emulated disk after the unplug, as it should be.
> 
> Yeah. What I meant is that we should make sure that a misbehaving guest,
> which just keeps on playing with the IDE ports anyway, can't crash qemu.
> A quick review suggests that it is the case, but testing it anyway would
> be better.

I see what you mean: I tested it, a guest cannot crash Qemu.